Heat exchanger comprising a core of tubes

ABSTRACT

The invention concerns a heat exchanger ( 1 ) comprising an inlet tank ( 2 ), having a fluid inlet ( 4 ),and an outlet tank ( 3 ), having a fluid outlet ( 5 ),and a core ( 6 ) of tubes ( 7, 8 ) joining said inlet tank ( 2 ) and said outlet tank ( 3 ) together and creating a plurality of fluid flow paths (P 1 ) from said inlet tank ( 2 ) to said outlet tank ( 3 ), wherein said tubes ( 7, 8 ) belong to a primary and a secondary group of tubes( 7, 8 ). According to the invention said inlet tank ( 2 ) and said outlet tank ( 3 ) have header plates( 9, 10 ), which form core interfaces and comprise throughout identical tube insertion orifices for both the primary group of tubes ( 7 ) and the secondary group of tubes ( 8 ).Further, the tubes being a member of the primary group are base tubes ( 7 )and the tubes being a member of the secondary group are adaptation tubes ( 8 ), which differ from the base tubes ( 7 ) and a reused to locally change properties of the heat exchanger ( 1 ) in critical areas of the heat exchanger ( 1 ).

TECHNICAL FIELD

The present invention concerns a heat exchanger comprising an inlettank, having a fluid inlet for a fluid, and an outlet tank, having afluid outlet for said fluid, and a core of tubes joining said inlet tankand said outlet tank together and creating a plurality of fluid flowpaths for said fluid from said inlet tank to said outlet tank, whereinsaid tubes belong to a primary and a secondary group of tubes.

PRIOR ART

A heat exchanger according to the preamble is known from the patent U.S.Pat. No. 4,791,982. The heat exchanger revealed in that patent is acoolant radiator which has a core comprising tubes belonging to aprimary and a secondary group of tubes. There is a difference in tubesize between the two groups, which is used mainly to improve flowdistribution and hence efficiency especially at low flow rates.

OBJECT OF THE INVENTION

A drawback of the prior art heat exchanger is that its technical conceptis rather limited when it comes to versatility. Since it comprises useof differently sized tubes, it necessitates use of header plates havingtube insertion orifices, which are sized and placed according to aunique pattern for each series of heat exchangers. This makes productionof small series of heat exchangers inefficient and hampers productionversatility. Against that background an object of the present inventionis to improve the known heat exchanger, such that production thereof issimplified and in particular rendered more efficient and versatile.

SUMMARY OF THE INVENTION

According to the invention this is achieved by means of a heat exchangeraccording to the preamble, said heat exchanger being characterized inthat said inlet tank and said outlet tank have header plates, which formcore interfaces and comprise throughout identical tube insertionorifices for both the primary group of tubes and the secondary group oftubes, in that the tubes being a member of the primary group are basetubes, and in that the tubes being a member of the secondary group areadaptation tubes, which differ from the base tubes and are used tolocally change properties of the heat exchanger in critical areas of theheat exchanger, and.

Use of header plates with throughout identical tube insertion orifices,does of course necessitate use of tubes having a throughout identicalouter shape, as they otherwise would not fit the header plates. This ishowever no problem, as tube characteristics can be varied internally indifferent ways, e.g. by choosing an appropriate tube wall thickness, byproviding dimples or turbulators or by using different tube inserts.Hence, the invention renders it possible for instance to efficientlyproduce small series of adapted heat exchangers by means of identicalheader plates but different tubes at chosen positions.

According to one embodiment said secondary group of tubes in order toprolong life of the heat exchanger comprises adaptation tubes eachproviding an enhanced strength compared to a basic strength provided byeach one of said base tubes, wherein said adaptation tubes are used inareas of the heat exchanger where stress levels tend to be higher than amedium stress level of the entire heat exchanger. Areas of a heatexchanger where such strengthening tubes are useful are e.g. cornerareas of a substantially parellelepipedic heat exchanger core.

According to a further embodiment said adaptation tubes can provide anenhanced strength by having a wall thickness exceeding a wall thicknessof the base tubes. Increasing tube wall thickness is an easy way toenhance strength, but if the tubes are sheet metal pipes, which isnormal procedure in the art, it requires use of differently gauged sheetmetal for the tubes pertaining to the first and the second group,respectively.

According to a further embodiment said adaptation tubes provide anenhanced strength by comprising stiffening inserts arranged in tubeopenings. Providing stiffening inserts is also an easy way to enhancestrength and makes use of tubes having an identical wall thicknesspossible. However, production, insertion and fastening of suchstiffening inserts are aspects to be considered.

According to a further embodiment said adaptation tubes provide anenhanced strength by comprising stiffer turbulators than turbulatorsarranged in said base tubes. In the art use of so-called turbulatorsinside of heat exchanger tubes is quite common. In the light of this,use of differently designed turbulators to achieve a heat exchangeraccording to the invention is an attractive solution.

According to a further embodiment said adaptation tubes provide anenhanced strength by comprising internal stiffening ribs. Internalstiffening ribs can be provided e.g. by embossing sheet metal, of whichtubes are produced, accordingly.

According to a further embodiment said adaptation tubes provide anenhanced strength by comprising extra durable tube seams created bymeans of all smooth tube walls. When producing tubes of sheet metal, abrazing seam running along the tube is created. This seam is renderedmore durable if the original sheet is all smooth and void of forinstance embossed dimples.

According to a further embodiment said heat exchanger comprises a firstrow of tubes and a second row of tubes, wherein at least a plurality ofthe tubes of the first row belong to the primary group of tubes and alltubes of the second row belong to the secondary group of tubes. Asolution like this can be advantageous for instance if the heatexchanger is a coolant radiator which is bolted to another unit, such asa charged air cooler, which helps stabilizing the coolant radiator tuberow next to it.

According to a further embodiment said secondary group of tubes in orderto improve efficiency of the heat exchanger comprises adaptation tubes,each providing a lower flow resistance than a flow resistance providedby each one of said base tubes, wherein said adaptation tubes arearranged in areas of the heat exchanger where fluid flow levels tend tobe lower than a medium fluid flow level of the entire heat exchanger.Areas of a heat exchanger where low flow tends to be a problem aremainly areas remote of a fluid in or outlet, areas in the shadow ofbrackets or the like, and areas immediately beneath a fluid inlet.

According to a further embodiment said adaptation tubes provide a lowerflow resistance by comprising turbulators causing a lower flowresistance than turbulators being arranged in said base tubes. Asindicated before, turbulators inside of heat exchanger tubes are quitecommon, and, thus, use of differently designed turbulators to achieve aheat exchanger according to the invention is an attractive solution.

According to a further embodiment said adaptation tubes provide a lowerflow resistance by having all smooth walls, while said base tubes havedimpled walls. In the art dimples are used to promote heat exchange.However, dimples do also cause some extra flow resistance, which caneffectively be avoided by all smooth tube walls.

According to a further embodiment said heat exchanger comprises a firstrow of tubes and a second row of tubes, wherein all tubes of the firstrow belong to the secondary group of tubes and all tubes of the secondrow belong to the primary group of tubes. A solution like this can beadvantageous for instance if the fluid inlet and outlet of the heatexchanger tend to promote flow through the second row.

According to a further embodiment said secondary group comprisesadaptation tubes, each providing a lower flow resistance than a flowresistance provided by each one of said base tubes, wherein saidadaptation tubes are arranged in the heat exchanger in an alternatingpattern mixed with base tubes. A solution like this is advantageous forinstance if fluid flow through the heat exchanger is highly dependent onrpm of an engine cooled by means of the heat exchanger. In such a casealternate tubes in a certain pattern help promoting an even flow offluid through the entire heat exchanger.

According to a further embodiment said adaptation tubes provide a lowerflow resistance by comprising turbulators causing a lower flowresistance than turbulators being arranged in said base tubes. Theadvantage of different turbulators has already been discussed in theabove.

According to a further embodiment said adaptation tubes provide a lowerflow resistance by having all smooth walls, while said base tubes havedimpled walls. As indicated before, dimples cause some extra flowresistance, which can effectively be avoided by all smooth tube walls.

According to a further embodiment said alternating pattern comprises arow of alternatingly a base tube and an adaptation tube. In someinstances it shows to be advantageous to mix tubes in the indicated wayto arrive at an optimum fluid flow distribution at all fluid flow rates.

According to a further embodiment said alternating pattern comprises arow of alternatingly two base tubes and an adaptation tube. Again, thepurpose of such a solution is to optimize performance of a heatexchanger, especially at low to high fluid flow rates.

According to a further embodiment said secondary group of tubes issubdivided into at least two kinds of differently designed tubes. Use ofdifferently designed tubes for the second group of tubes furtherenhances versatility of the heat exchanger according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings embodiments of heat exchangers according to theinvention are shown schematically. In the drawings:

FIG. 1 is a view from behind and shows a heat exchanger in the form of acoolant radiator;

FIGS. 2 to 13 are views from top and show portions of header plates ofdifferent embodiments of the coolant radiator of FIG. 1;

FIG. 14 is a view from front and shows a heat exchanger in the form of acharged air cooler; and

FIGS. 15 to 20 are views from a side and show portions of header platesof different embodiments of the charged air cooler of FIG. 14.

DESCRIPTION OF A PREFERRED EMBODIMENT

In the following preferred embodiments of the invention are describedwith reference being had to the drawings. In the drawings like referencesigns indicate similar elements.

In FIG. 1 a heat exchanger 1 is shown in a back view. The heat exchanger1 shown is a coolant radiator, which has a top inlet tank 2 and a bottomoutlet tank 3. Between these is a parallelepipedic radiator core 6,which comprises a plurality of vertical tubes 7, 8 and fins (not shown)there between. The tubes 7, 8 are tightly connected to the tanks 2, 3 bymeans of header plates 9, 10 of the tanks 2, 3 and are used to leadcoolant from a fluid inlet 4 on the inlet tank 2 to a fluid outlet 5 onthe outlet tank 3 while being cooled on its way along fluid flow pathsillustrated by means of an arrow P.

Portions of the top plate 9 of the heat exchanger 1 are illustrated ingreater detail in FIGS. 2 to 13. In these figures different embodimentsof the heat exchanger 1 according to the invention are shown when viewedfrom above inside the top tank 2. The corresponding view of the oppositeor bottom header plate 10 is often identical but need not be. However,having studied the description a person skilled in the art will anywayknow how to best implement the present invention.

In order to enhance cooling, tubes 7, 8 of the coolant radiator cancomprise dimples, which are shown in FIGS. 2 to 13, where they aregenerally depicted 12. The dimples 12 are formed by stamping of the tubesheet metal prior to final assembly of the tubes 7, 8 into their flatshape. As can be seen in FIGS. 2 to 13 said dimples 12 form smallprotrusions inside of the tubes 7, 8. The dimples 12 influence fluidflow inside of the tubes 7, 8 by causing turbulence, which is beneficialfor heat exchange but rises pressure drop. Hence, in order to create anoptimal heat exchanger 1, it is important to tune the heat exchanger 1such that heat exchange is maximized while pressure drop is kept low,especially at different flow rates of the fluid passing trough the tubes7, 8 along said fluid flow paths P.

To render that possible in an effective way the header plates 9, 10 ofthe heat exchanger 1 according to the invention comprise throughoutidentical tube insertion orifices 11. In these tubes 7, 8 belonging to aprimary and a secondary group of differently designed tubes are insertedin a tightly fitting way and fastened, e. g. by brazing.

The tubes 7 belonging to said primary group are in this context calledbase tubes 7, as they so to say fulfill basic heat exchange demands of aheat exchanger 1. The tubes 8 belonging to said secondary group are inthis context instead called adaptation tubes 8, as they are used tolocally change properties of the heat exchanger 1 in critical areas.Where these critical areas are to be found and how they are dealt withaccording to the invention is explained below by means of examplesrelating only to the top header plate 9.

The header plates 9 of FIGS. 2 to 13 reveal that all embodiments of theheat exchanger 1 shown in the drawings illustrate a two row coolantradiator. However, this does not have to be the case and is chosen onlyto exemplify some typical layout solutions within the frame of theinvention as claimed. In other words, one single row of tubes 7, 8 ormultiple rows of tubes 7, 8 as well as tubes 7, 8 turned in another wayin relation to the header plates 9 are also within the scope.

FIG. 2 is used to illustrate an end portion, such as the top leftportion of a heat exchanger 1 of FIG. 1. As can be seen, of the totallytwenty tubes shown in FIG. 2, the fourteen to the right (seven per row)are depicted 7. Hence they are so-called base tubes 7 of the primarygroup of tubes, which in this case means that they have a standard tubewall thickness and dimples 12 on the inside. The remaining six tubes tothe left (three per row) are instead so-called adaptation tubes 8 of thesecondary group, which in this case means that they have a greater tubewall thickness and dimples 12 on the inside. The adaptation tubes 8 helpstabilizing the heat exchanger 1 corner, where stress usually is higher,but rises pressure drop to a certain extent.

FIG. 3 illustrates a mid section somewhere along a header plate 9. Thistime a group of eight adaptation tubes 8 (four per row) corresponding tothe ones of FIG. 2 are arranged amid the base tubes 7. Again the purposeis to stabilize the heat exchanger 1 or alternatively to limit flow offluid by causing an increased pressure drop, or both.

FIGS. 4 and 5 do also illustrate a mid section somewhere along a headerplate 9. The tubes 7 and 8 belonging to the primary and secondary groupcorrespond to the ones described above and are arranged in analternating pattern comprising rows of alternatingly a base tube 7 and aadaptation tube 8 or rows of alternatingly two base tubes 7 and aadaptation tube 8. By causing different pressure drops, the tubes 7, 8help distribute flow evenly over the entire heat exchanger 1, especiallyat low fluid flow rates, which helps improving efficiency. However, theadaptation tubes 8 with their thicker gauge are of course beneficial forheat exchanger integrity as well.

FIG. 6 illustrates an arbitrary section along a header plate 9, whileFIG. 7 illustrates an end or corner portion, such as a top left end orcorner portion of the heat exchanger 1 of FIG. 1. In both embodimentsbase tubes 7 and adaptation tubes 8 of the same kind as before are used,that is base tubes 7 with a standard wall gauge and adaptation tubes 8with a greater wall gauge.

In the embodiment of FIG. 6 there is one row of solely base tubes 7 andone row of solely adaptation tubes 8. The base tube row is preferablyarranged close to a solid support, such as a charged air cooler, whichhelps withstand outer forces, while the more exposed part of the heatexchanger 1 shows reinforced tubes 8 only. The embodiment of FIG. 7 ismuch alike, differing only in that just a few tubes in a corner portionof the heat exchanger 1 comprise strong adaptation tubes 8, such as acorner holding a fastening bracket (not shown). In that way it ispossible to preserve heat exchanger integrity without causing excessivepressure drop.

In FIG. 8 the base tubes 7 are again formed by dimpled tubes having astandard wall thickness and being arranged for instance in a mid sectoralong a header plate 9. The adaptation tubes 8, which for instance arearranged at an end portion of the header plate 9, are this time formedby all flat tubes void of any dimples. That makes it possible tostrengthen the tubes 8 thanks to a smooth unaffected brazing seem, whichis indicated by means of an arrow 13.

An adaptation tube 8 of this kind renders it possible to strengthen thestructure without a pressure drop increase or a thicker tube wallthickness, but lessens heat rejection to some extent.

In the embodiment shown in FIG. 9 the same kinds of tubes 7, 8 are usedas in the embodiment in FIG. 8. The difference lies in that this timethere is a row with only dimpled base tubes 7 and all flat adaptationtubes 8. As described before, such a row solution can be used toinfluence fluid flow, in strengthening purposes, or both.

FIGS. 10 and 11 reveal embodiments, which show that the group ofadaptation tubes 8 can comprise more than one different kind ofadaptation tubes, such as two in FIG. 10 and three in FIG. 11. As beforethere are standard dimpled base tubes 7, which in the embodiment of FIG.10 are arranged e.g. in a mid section along a header plate 9 of a heatexchanger 1, and in the embodiment of FIG. 11 are arranged in a midsection, too, but only in one of two rows of tubes of a heat exchanger1. In FIG. 10 the remaining tubes, that is the adaptation tubes 8 at anend of the header plate 9 in question, comprise both eight outer tubes 8with an extremely thick tube wall but yet provided with dimples 11, andsix intermediate tubes 8 with a not quite as thick tube wall and dimplesbetween said outer tubes 8 and said base tubes 7. In FIG. 11 the dimpledbase tubes 7 are arranged in just one row in a mid sector of a headerplate 9 of a two row heat exchanger. To their left in the embodimentshown in FIG. 11 and in the same row there are dimpled adaptation tubes8 having a greater wall thickness. In the other row next to the basetubes 7 there are all smooth adaptation tubes 8 having a wall thicknesscorresponding to the one of the base tubes 7. Further, in the other rownext to the dimpled adaptation tubes 8 again there are all smoothadaptation tubes 8, but these have a greater wall thickness than theones next to the base tubes 7. In common the embodiments of FIGS. 10 and11 show that there are few limits when it comes to optimizing a heatexchanger 1 by means of the invention, irrespective if one wishes tobetter mechanical strength or life of a heat exchanger or betterefficiency or performance of a heat exchanger.

In FIG. 12 a further embodiment of a heat exchanger 1 according to theinvention is illustrated. As before the header plate 9 shown in FIG. 12has throughout identical tube insertion orifices 12. In these arefastened dimpled base tubes 7 in two rows to the right of eight (four ineach row) adaptation tubes 8. These can be smooth or dimpled but have anend portion which enables insertion of a strengthening tube insert 14.The tube insert 14 is adapted to be brazed to the tube 8 and stiffenssaid end portion considerably without affecting fluid flow all too much.

In FIG. 13 a final embodiment of a header plate 9 of the heat exchanger1 of FIG. 1 is shown. The kind and placement of the base tubes 7corresponds exactly to the embodiment of FIG. 12. Hence, again theadaptation tubes 8 are the ones that differ. This time they provide anenhanced strength by comprising internal stiffening ribs 15, which canbe stamped just like dimples 12. Preferably the stiffening ribs 15 ofthe adaptation tubes 8 meat in a central part of the tubes 8 andinterconnect by means of a brazing seam (not depicted). Influence onfluid flow is comparable to the one of the dimpled base tubes 7. Inother words, the purpose of these adaptation tubes 8 in mainly astructural one.

I FIG. 14 a heat exchanger 21 is shown in a front view. The heatexchanger 21 shown is a charged air cooler (CAC), which has a left inlettank 22 and a right outlet tank 23. Between these is a parallelepipedicCAC core 26, which comprises a plurality of horizontal tubes 27, 28 andfins (not shown) there between. The tubes 27, 28 are tightly connectedto the tanks 22, 23 by means of header plates 29, 30 and are used tolead charged air from a fluid inlet 24 on the inlet tank 22 to a fluidoutlet 25 on the outlet tank 23 while being cooled on its way alongfluid flow paths illustrated by means of an arrow P.

In order to enhance cooling, the tubes 27, 28 of a CAC 21 are usuallyprovided with turbulators, by which are meant formed metal sheet insertsbrazed to the inside of said tubes. In the drawings in FIGS. 15 to 20the turbulators are generally depicted 32, 33 and shown to besubstantially corrugated. However, in reality they can have a totallydifferent shape. Therefore the versions shown in FIGS. 15 to 20 are onlyto be viewed as mere examples.

Depending on temperatures, pressures and geometry, in a CAC 21 fluidflow through different tubes 27, 28 of the CAC core 26 is difficult todistribute evenly. Due to rather high temperatures in a CAC 21, this caneasily lead to structural failure. Further, inefficiently used tubes 27,28 do lower overall efficiency.

To mitigate these problems tanks 22, 23 of a CAC 21 usually are formedsuch that they taper from a fluid inlet 24 or fluid outlet 25, but thatmeasure alone does not really suffice. Hence, according to the principleof the present invention even for the CAC heat exchanger 21 tubes 27, 28belonging to two different groups of tubes are used for flow andtemperature tuning and structural integrity. How this is done isillustrated by means of the embodiments shown in FIGS. 15 to 20.

In FIG. 15 a portion of the left header plate 29 of FIG. 14 is shown.The corresponding view of the opposite or right header plate 30 is oftenidentical but need not be. However, having studied the description aperson skilled in the art will anyway know how to best implement thepresent invention.

The header plate 29 comprises a number of identical tube insertionorifices 31, in which tubes 27, 28 fit tightly by being brazed orwelded. The insertion orifices 31 are in this case arranged horizontallyand in a single row, one above the other. However, they could also bearranged vertically and/or in two or more rows.

In FIG. 15 the bottom three tubes are so-called base tubes 27 whichbelong to a primary group of tubes, whereas the top three tubes areso-called adaptation tubes 28 and belong to a secondary group of tubes.The base tubes 27 and adaptation tubes 28 differ in that they comprisedifferently shaped turbulators 32, 33. The ones 32 of the base tubes 27show a wide undulation pattern, which gives them a lower heatdissipation capacity than the more narrowly undulated turbulators 33 ofthe adaptation tubes 28. On the other hand, due the turbulators 33 theadaptation tubes 28 cause a higher pressure drop, which makes fluid moreprone to pass through the base tubes 27. In other words the adaptationtubes can be used to steer excessive fluid flow away from parts of theCAC, such as highly loaded parts close to the fluid inlet 24.

The embodiment of FIG. 16 is quite similar to the one of FIG. 15. Itdiffers only in that the undulations of the turbulators 32 of the basetubes 27 are undulated just as narrow as the ones 33 of the adaptationtubes 28. However, the turbulators 33 of the adaptations tubes 28 aremade of a thicker metal sheet, which leads to the desired differencebetween the two types of tubes 27, 28, with an extra emphasis ondurability.

In FIG. 17 the bottom three tubes are base tubes 27 corresponding to theones of FIG. 16. In the top three or adaptation tubes 28, theturbulators 33 are much alike the turbulators 32 of the base tubes 27but have curled flanges 34 which stiffen short sides of the adaptationtubes 28. Said flanges 34 do hardly influence fluid flow, which meansthis embodiment mainly is suited to extend life in critical areas of aCAC 21.

In FIGS. 18 and 19 the bottom three tubes are base tubes 27 belonging tothe primary group of tubes. As in some other cases before they differ inthat their turbulators 32, 33 show differently wide undulations. The topthree tubes in both figures are instead alike and comprise identicallyundulated turbulators as well as tubular stiffening inserts 35 fittingexactly into the adaptation tubes 28. The stiffening inserts 35 doinfluence fluid flow and lead to an enhanced strength. Hence use oftubes 27, 28 according to the embodiments of FIGS. 18 and 19 isadvantageous in heat exchanger areas where load is high, such as next toan inlet 24.

In the final drawing figure, FIG. 20, there are three base tubes 27 atthe bottom and three adaptation tubes 28 at the top, all tubes 27, 28according to the present invention being inserted in identical tubeinsertion orifices 31 of a header plate 29. The turbulators 32, 33,which are inserted in both types of tubes are substantially alike,except for the fact that the ones 33 in the adaptation tubes 28 are alittle smaller. This is due to the fact that the adaptation tubes 28have a greater wall thickness than the base tubes 27. This limits fluidflow to some degree but leads to an enhanced overall strength.

A person skilled in the art is aware that alterations of the embodimentsdescribed are possible within the scope of the appended claims.

1. A heat exchanger comprising one inlet tank, having a fluid inlet fora fluid, and one outlet tank, having a fluid outlet for said fluid, anda core of tubes joining said one inlet tank and said one outlet tanktogether and creating a plurality of fluid flow paths for said fluidfrom said one inlet tank to said one outlet tank, wherein said tubesbelong to a primary and a secondary group of tubes, wherein said oneinlet tank comprises a first header plate, which forms a core interfaceof said one inlet tank, wherein said one outlet tank comprises a secondheader plate, which forms a core interface of said one outlet tank,wherein said first and second header plates comprise throughoutidentical tube insertion orifices for both the primary group of tubesand the secondary group of tubes, and wherein the tubes being a memberof the primary group are base tubes, and the tubes being a member of thesecondary group are adaptation tubes, which are designed differentlythan the base tubes of the primary group and are used to locally changeproperties of the heat exchanger in critical areas of the heatexchanger.
 2. The heat exchanger according to claim 1, wherein saidsecondary group in order to prolong life of the heat exchanger comprisesadaptation tubes each providing an enhanced strength compared to a basicstrength provided by each one of said base tubes, wherein saidadaptation tubes are used in areas of the heat exchanger where stresslevels tend to be higher than a medium stress level of the entire heatexchanger.
 3. The heat exchanger according to claim 2, wherein saidadaptation tubes provide an enhanced strength by having a wall thicknessexceeding a wall thickness of the base tubes.
 4. The heat exchangeraccording to claim 2, wherein said adaptation tubes provide an enhancedstrength by comprising stiffening inserts arranged in tube openings. 5.The heat exchanger according to claim 2, wherein said adaptation tubesprovide an enhanced strength by comprising first turbulators that arestiffer than second turbulators arranged in said base tubes.
 6. The heatexchanger according to claim 2, wherein said adaptation tubes provide anenhanced strength by comprising internal stiffening ribs.
 7. The heatexchanger according to claim 2, wherein said adaptation tubes provide anenhanced strength by comprising extra durable tube seams created by allsmooth tube walls.
 8. The heat exchanger according to claim 2, whereinsaid heat exchanger comprises a first row of tubes and a second row oftubes, and wherein at least a plurality of the tubes of the first rowbelong to the primary group of tubes and all tubes of the second rowbelong to the secondary group of tubes.
 9. The heat exchanger accordingto claim 1, wherein said secondary group in order to improve efficiencyof the heat exchanger comprises adaptation tubes, each providing a firstflow resistance that is lower than a second flow resistance provided byeach one of said base tubes, wherein said adaptation tubes are arrangedin areas of the heat exchanger where fluid flow levels tend to be lowerthan a medium fluid flow level of the entire heat exchanger.
 10. Theheat exchanger according to claim 9, wherein said adaptation tubesprovide a lower flow resistance by comprising first turbulators thatcause a lower flow resistance than second turbulators being arranged insaid base tubes.
 11. The heat exchanger according to claim 9, whereinsaid adaptation tubes provide a lower flow resistance by having allsmooth walls, while said base tubes have dimpled walls.
 12. The heatexchanger according to claim 9, wherein said heat exchanger comprises afirst row of tubes and a second row of tubes, and wherein all tubes ofthe first row belong to the secondary group of tubes and all tubes ofthe second row belong to the primary group of tubes.
 13. The heatexchanger according to claim 1, wherein said secondary group comprisesadaptation tubes, each providing a lower flow resistance than a flowresistance provided by each one of said base tubes, wherein saidadaptation tubes are arranged in the heat exchanger in an alternatingpattern mixed with base tubes.
 14. The heat exchanger according to claim13, wherein said adaptation tubes provide a lower flow resistance bycomprising first turbulators that cause a lower flow resistance thansecond turbulators being arranged in said base tubes.
 15. The heatexchanger according to claim 13, wherein said adaptation tubes provide alower flow resistance by having all smooth walls, while said base tubeshave dimpled walls.
 16. The heat exchanger according to claim 13,wherein said alternating pattern comprises a row of alternatingly a basetube and an adaptation tube.
 17. The heat exchanger according to claim13, wherein said alternating pattern comprises a row of alternatinglytwo base tubes and an adaptation tube.
 18. The heat exchanger accordingto claim 1, wherein said secondary group of tubes is subdivided into atleast two kinds of differently designed tubes.